【Spring源码分析】非懒加载的单例Bean初始化前后的一些操作

前言

之前两篇文章【Spring源码分析】非懒加载的单例Bean初始化过程（上篇）和【Spring源码分析】非懒加载的单例Bean初始化过程（下篇）比较详细地分析了非懒加载的单例Bean的初始化过程，整个流程始于AbstractApplicationContext的refresh()方法：

public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
        // Prepare this context for refreshing.
        prepareRefresh();

        // Tell the subclass to refresh the internal bean factory.
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

        // Prepare the bean factory for use in this context.
        prepareBeanFactory(beanFactory);

        try {
            // Allows post-processing of the bean factory in context subclasses.
            postProcessBeanFactory(beanFactory);

            // Invoke factory processors registered as beans in the context.
            invokeBeanFactoryPostProcessors(beanFactory);

            // Register bean processors that intercept bean creation.
            registerBeanPostProcessors(beanFactory);

            // Initialize message source for this context.
            initMessageSource();

            // Initialize event multicaster for this context.
            initApplicationEventMulticaster();

            // Initialize other special beans in specific context subclasses.
            onRefresh();

            // Check for listener beans and register them.
            registerListeners();

            // Instantiate all remaining (non-lazy-init) singletons.
            finishBeanFactoryInitialization(beanFactory);

            // Last step: publish corresponding event.
            finishRefresh();
        }

        catch (BeansException ex) {
            // Destroy already created singletons to avoid dangling resources.
            destroyBeans();

            // Reset 'active' flag.
            cancelRefresh(ex);

            // Propagate exception to caller.
            throw ex;
        }
    }
}

之前重点分析的是finishBeanFactoryInitialization方法，这个方法完成了所有非懒加载的单例Bean的初始化。今天我回头重看了一下refresh()方法，发现前面有一些方法还是忽略了没有去特别在意，其实他们都是Spring整个启动流程中的重要组成部分，下面就来分析一下finishBeanFactoryInitialization方法前面的一些方法。

obtainFreshBeanFactory方法之前已经详细分析过了，就从prepareBeanFactory方法开始。

PrepareBeanFactory方法

看一下PrepareBeanFactory方法的实现：

 1 protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
 2     // Tell the internal bean factory to use the context's class loader etc.
 3     beanFactory.setBeanClassLoader(getClassLoader());
 4     beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver());
 5     beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this));
 6 
 7     // Configure the bean factory with context callbacks.
 8     beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
 9     beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
10     beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
11     beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
12     beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
13 
14     // BeanFactory interface not registered as resolvable type in a plain factory.
15     // MessageSource registered (and found for autowiring) as a bean.
16     beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
17     beanFactory.registerResolvableDependency(ResourceLoader.class, this);
18     beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
19     beanFactory.registerResolvableDependency(ApplicationContext.class, this);
20 
21     // Detect a LoadTimeWeaver and prepare for weaving, if found.
22     if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
23         beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
24         // Set a temporary ClassLoader for type matching.
25         beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
26     }
27 
28     // Register default environment beans.
29     if (!beanFactory.containsBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
30         Map systemProperties;
31         try {
32             systemProperties = System.getProperties();
33         }
34         catch (AccessControlException ex) {
35             systemProperties = new ReadOnlySystemAttributesMap() {
36                 @Override
37                 protected String getSystemAttribute(String propertyName) {
38                     try {
39                         return System.getProperty(propertyName);
40                     }
41                     catch (AccessControlException ex) {
42                         if (logger.isInfoEnabled()) {
43                             logger.info("Not allowed to obtain system property [" + propertyName + "]: " +
44                                     ex.getMessage());
45                         }
46                         return null;
47                     }
48                 }
49             };
50         }
51         beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, systemProperties);
52     }
53 
54     if (!beanFactory.containsBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
55         Map<String,String> systemEnvironment;
56         try {
57             systemEnvironment = System.getenv();
58         }
59         catch (AccessControlException ex) {
60             systemEnvironment = new ReadOnlySystemAttributesMap() {
61                 @Override
62                 protected String getSystemAttribute(String variableName) {
63                     try {
64                         return System.getenv(variableName);
65                     }
66                     catch (AccessControlException ex) {
67                         if (logger.isInfoEnabled()) {
68                             logger.info("Not allowed to obtain system environment variable [" + variableName + "]: " +
69                                     ex.getMessage());
70                         }
71                         return null;
72                     }
73                 }
74             };
75         }
76         beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, systemEnvironment);
77     }
78 }

首先是第3行，配置当前上下文ClassLoader

接着是第4行，这是一个表达是语言处理器，可以使用#{bean.xxx}的方式来调用相关属性值

接着是第5行，这是一个属性编辑器，具体没怎么用过

接着是第8行，第8行增加了一个ApplicationContextAwareProcessor用于上下文回调，它是BeanPostProcessor的实现类，跟一下这个接口的两个方法postProcessBeforeInitialization和postProcessAfterInitialization即可知道这个方法的作用是：

如果Bean是EmbeddedValueResolverAware接口的实现类，则调用setEmbeddedValueResolver方法，传入当前BeanFactory
如果Bean是ResourceLoaderAware接口的实现类，则调用setResourceLoader方法，传入当前上下文ApplicationContext
如果Bean是ApplicationEventPublisherAware的实现类，则调用setApplicationEventPublisher方法，传入当前上下文ApplicationContext
如果Bean是MessageSourceAware的实现类，则调用setMessageSource方法，传入当前上下文ApplicationContext
如果Bean是ApplicationContextAware的实现类，则调用setApplicationContext方法，传入当前上下文ApplicationContext

接着是第9行~第12行，意思是Bean如果是这些接口的实现类，则不会被自动装配，自动装配见【Spring9】Autowire（自动装配）机制

接着是第16行~第19行，意思是修正依赖，这里是一些自动装配的特殊规则，比如是BeanFactory接口的实现类，则修正为当前BeanFactory

接着是第22行~第26行，意思是如果自定义的Bean中有定义过一个名为"loadTimeWeaver"的Bean，则会添加一个LoadTimeWeaverAwareProcessor

最后是第29行~第77行，意思是如果自定义的Bean中没有名为"systemProperties"和"systemEnvironment"的Bean，则注册两个Bena，Key为"systemProperties"和"systemEnvironment"，Value为Map，这两个Bean就是一些系统配置和系统环境信息，具体可以写这么一段代码测试一下：

public class TestSpring {
    
    @SuppressWarnings("unchecked")
    @Test
    public void testSpring() {
        ApplicationContext ac = new ClassPathXmlApplicationContext("spring/spring.xml");
        
        Map<String, String> systemPropertiesBean = (Map<String, String>)ac.getBean("systemProperties");
        for (Map.Entry<String, String> entry : systemPropertiesBean.entrySet()) {
            System.out.println(entry.getKey() + "--->" + entry.getValue());
        }
        
        System.out.println("==============================华丽的分隔符==============================");
        Map<String, String> systemEnvironmentBean = (Map<String, String>)ac.getBean("systemEnvironment");
        for (Map.Entry<String, String> entry : systemEnvironmentBean.entrySet()) {
            System.out.println(entry.getKey() + "--->" + entry.getValue());
        }
    }
    
}

涉及个人信息，运行结果我就不贴了，大家可以自己试试，至此整个PrepareBeanFactory方法的细节已经分析完毕了。

invokeBeanFactoryPostProcessors方法

这个是整个Spring流程中非常重要的一部分，是Spring留给用户的一个非常有用的扩展点，BeanPostProcessor接口针对的是每个Bean初始化前后做的操作而BeanFactoryPostProcessor接口针对的是所有Bean实例化前的操作，注意用词，初始化只是实例化的一部分，表示的是调用Bean的初始化方法，BeanFactoryPostProcessor接口方法调用时机是任意一个自定义的Bean被反射生成出来前。

OK，看一下源码：

 1 protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
 2     // Invoke BeanDefinitionRegistryPostProcessors first, if any.
 3     Set<String> processedBeans = new HashSet<String>();
 4     if (beanFactory instanceof BeanDefinitionRegistry) {
 5         BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
 6         List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
 7         List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =
 8                 new LinkedList<BeanDefinitionRegistryPostProcessor>();
 9         for (BeanFactoryPostProcessor postProcessor : getBeanFactoryPostProcessors()) {
10             if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
11                 BeanDefinitionRegistryPostProcessor registryPostProcessor =
12                             (BeanDefinitionRegistryPostProcessor) postProcessor;
13                     registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
14                     registryPostProcessors.add(registryPostProcessor);
15             }
16             else {
17                 regularPostProcessors.add(postProcessor);
18             }
19         }
20         Map<String, BeanDefinitionRegistryPostProcessor> beanMap =
21                 beanFactory.getBeansOfType(BeanDefinitionRegistryPostProcessor.class, true, false);
22         List<BeanDefinitionRegistryPostProcessor> registryPostProcessorBeans =
23                 new ArrayList<BeanDefinitionRegistryPostProcessor>(beanMap.values());
24         OrderComparator.sort(registryPostProcessorBeans);
25         for (BeanDefinitionRegistryPostProcessor postProcessor : registryPostProcessorBeans) {
26             postProcessor.postProcessBeanDefinitionRegistry(registry);
27         }
28         invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);
29         invokeBeanFactoryPostProcessors(registryPostProcessorBeans, beanFactory);
30         invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
31         processedBeans.addAll(beanMap.keySet());
32     }
33     else {
34         // Invoke factory processors registered with the context instance.
35         invokeBeanFactoryPostProcessors(getBeanFactoryPostProcessors(), beanFactory);
36     }
37 
38     // Do not initialize FactoryBeans here: We need to leave all regular beans
39     // uninitialized to let the bean factory post-processors apply to them!
40     String[] postProcessorNames =
41         beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
42 
43     // Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
44     // Ordered, and the rest.
45     List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
46     List<String> orderedPostProcessorNames = new ArrayList<String>();
47     List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
48     for (String ppName : postProcessorNames) {
49         if (processedBeans.contains(ppName)) {
50             // skip - already processed in first phase above
51         }
52         else if (isTypeMatch(ppName, PriorityOrdered.class)) {
53             priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
54         }
55         else if (isTypeMatch(ppName, Ordered.class)) {
56             orderedPostProcessorNames.add(ppName);
57         }
58         else {
59             nonOrderedPostProcessorNames.add(ppName);
60         }
61     }
62 
63     // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
64     OrderComparator.sort(priorityOrderedPostProcessors);
65     invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
66 
67     // Next, invoke the BeanFactoryPostProcessors that implement Ordered.
68     List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
69     for (String postProcessorName : orderedPostProcessorNames) {
70         orderedPostProcessors.add(getBean(postProcessorName, BeanFactoryPostProcessor.class));
71     }
72     OrderComparator.sort(orderedPostProcessors);
73     invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
74 
75     // Finally, invoke all other BeanFactoryPostProcessors.
76     List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
77     for (String postProcessorName : nonOrderedPostProcessorNames) {
78         nonOrderedPostProcessors.add(getBean(postProcessorName, BeanFactoryPostProcessor.class));
79     }
80     invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
81 }

我们可以自己实现BeanFactoryPostProcessor接口并实现postProcessBeanFactory方法，在所有Bean加载的流程开始前，会调用一次postProcessBeanFactory方法。分析一下这段代码，首先我们使用的是DefaultListableBeanFactory，它是BeanDefinitionRegistry的子类，因此进入第4行的判断。

整个判断获取的是当前有的BeanFactoryPostProcessor并调用postProcessBeanFactory，这些BeanFactoryPostProcessor是前置通过AbstractApplicationContext的addBeanFactoryPostProcessor方法添加的而不是配置文件里面配置的BeanFactoryPostProcessor的实现Bean，因此这个判断没有任何可执行的BeanFactoryPostProcessor。

接着40行~41行这两行，获取的是beanDefinitionMap中的Bean，即用户自定义的Bean。

接着第45行~61行，这里分出了三个List，表示开发者可以自定义BeanFactoryPostProcessor的调用顺序，具体为调用顺序为：

如果BeanFactoryPostProcessor实现了PriorityOrdered接口（PriorityOrdered接口是Ordered的子接口，没有自己的接口方法定义，只是做一个标记，表示调用优先级高于Ordered接口的子接口），是优先级最高的调用，调用顺序是按照接口方法getOrder()的实现，对返回的int值从小到大进行排序，进行调用
如果BeanFactoryPostProcessor实现了Ordered接口，是优先级次高的调用，将在所有实现PriorityOrdered接口的BeanFactoryPostProcessor调用完毕之后，依据getOrder()的实现对返回的int值从小到大排序，进行调用
不实现Ordered接口的BeanFactoryPostProcessor在上面的BeanFactoryPostProcessor调用全部完毕之后进行调用，调用顺序就是Bean定义的顺序

最后的第63行~第80行就是按照上面的规则依次先将BeanFactoryPostProcessor接口对应的实现类实例化出来并调用postProcessBeanFactory方法。

registerBeanPostProcessors方法

接下来看看registerBeanPostProcessors方法，顾名思义，就是注册自定义的BeanPostProcessor接口。看一下代码实现：

 1 protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
 2     String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
 3 
 4     // Register BeanPostProcessorChecker that logs an info message when
 5     // a bean is created during BeanPostProcessor instantiation, i.e. when
 6     // a bean is not eligible for getting processed by all BeanPostProcessors.
 7     int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
 8     beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
 9 
10     // Separate between BeanPostProcessors that implement PriorityOrdered,
11     // Ordered, and the rest.
12     List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
13     List<BeanPostProcessor> internalPostProcessors = new ArrayList<BeanPostProcessor>();
14     List<String> orderedPostProcessorNames = new ArrayList<String>();
15     List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
16     for (String ppName : postProcessorNames) {
17         if (isTypeMatch(ppName, PriorityOrdered.class)) {
18             BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
19             priorityOrderedPostProcessors.add(pp);
20             if (pp instanceof MergedBeanDefinitionPostProcessor) {
21                 internalPostProcessors.add(pp);
22             }
23         }
24         else if (isTypeMatch(ppName, Ordered.class)) {
25             orderedPostProcessorNames.add(ppName);
26         }
27         else {
28             nonOrderedPostProcessorNames.add(ppName);
29         }
30     }
31 
32     // First, register the BeanPostProcessors that implement PriorityOrdered.
33     OrderComparator.sort(priorityOrderedPostProcessors);
34     registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
35 
36     // Next, register the BeanPostProcessors that implement Ordered.
37     List<BeanPostProcessor> orderedPostProcessors = new ArrayList<BeanPostProcessor>();
38     for (String ppName : orderedPostProcessorNames) {
39         BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
40         orderedPostProcessors.add(pp);
41         if (pp instanceof MergedBeanDefinitionPostProcessor) {
42             internalPostProcessors.add(pp);
43         }
44     }
45     OrderComparator.sort(orderedPostProcessors);
46     registerBeanPostProcessors(beanFactory, orderedPostProcessors);
47 
48     // Now, register all regular BeanPostProcessors.
49     List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
50     for (String ppName : nonOrderedPostProcessorNames) {
51         BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
52         nonOrderedPostProcessors.add(pp);
53         if (pp instanceof MergedBeanDefinitionPostProcessor) {
54             internalPostProcessors.add(pp);
55         }
56     }
57     registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
58 
59     // Finally, re-register all internal BeanPostProcessors.
60     OrderComparator.sort(internalPostProcessors);
61     registerBeanPostProcessors(beanFactory, internalPostProcessors);
62 
63     beanFactory.addBeanPostProcessor(new ApplicationListenerDetector());
64 }

整体代码思路和invokeBeanFactoryPostProcessors方法类似，但是这里不会调用BeanPostProcessor接口的方法，而是把每一个BeanPostProcessor接口实现类实例化出来并按照顺序放入一个List中，到时候按顺序进行调用。

具体代码思路可以参考invokeBeanFactoryPostProcessors，这里就根据代码总结一下BeanPostProcessor接口的调用顺序：

优先调用PriorityOrdered接口的子接口，调用顺序依照接口方法getOrder的返回值从小到大排序
其次调用Ordered接口的子接口，调用顺序依照接口方法getOrder的返回值从小到大排序
接着按照BeanPostProcessor实现类在配置文件中定义的顺序进行调用
最后调用MergedBeanDefinitionPostProcessor接口的实现Bean，同样按照在配置文件中定义的顺序进行调用

initMessageSource方法

initMessageSource方法用于初始化MessageSource，MessageSource是Spring定义的用于实现访问国际化的接口，看一下源码：

 1 protected void initMessageSource() {
 2     ConfigurableListableBeanFactory beanFactory = getBeanFactory();
 3     if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
 4         this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
 5         // Make MessageSource aware of parent MessageSource.
 6         if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
 7             HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
 8             if (hms.getParentMessageSource() == null) {
 9                 // Only set parent context as parent MessageSource if no parent MessageSource
10                 // registered already.
11                 hms.setParentMessageSource(getInternalParentMessageSource());
12             }
13         }
14         if (logger.isDebugEnabled()) {
15             logger.debug("Using MessageSource [" + this.messageSource + "]");
16         }
17     }
18     else {
19         // Use empty MessageSource to be able to accept getMessage calls.
20         DelegatingMessageSource dms = new DelegatingMessageSource();
21         dms.setParentMessageSource(getInternalParentMessageSource());
22         this.messageSource = dms;
23             beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
24         if (logger.isDebugEnabled()) {
25             logger.debug("Unable to locate MessageSource with name '" + MESSAGE_SOURCE_BEAN_NAME +
26                     "': using default [" + this.messageSource + "]");
27         }
28     }
29 }

这个if...else...判断比较好理解：

如果自定义了名为"messageSource"的Bean，那么直接实例化Bean，该Bean必须是MessageSource接口的实现Bean，顺便该Bean如果是HierarchicalMessageSource接口的实现类，强转为HierarchicalMessageSource接口，并设置一下parentMessageSource
如果没有自定义名为"messageSource"的Bean，那么会默认注册一个DelegatingMessageSource并加入

initApplicationEventMulticaster方法

initApplicationEventMulticaster方法是用于初始化上下文事件广播器的，看一下源码：

 1 protected void initApplicationEventMulticaster() {
 2     ConfigurableListableBeanFactory beanFactory = getBeanFactory();
 3     if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
 4         this.applicationEventMulticaster =
 5                 beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
 6         if (logger.isDebugEnabled()) {
 7             logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
 8         }
 9     }
10     else {
11         this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
12         beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
13         if (logger.isDebugEnabled()) {
14             logger.debug("Unable to locate ApplicationEventMulticaster with name '" +
15                     APPLICATION_EVENT_MULTICASTER_BEAN_NAME +
16                     "': using default [" + this.applicationEventMulticaster + "]");
17         }
18     }
19 }

和initMessageSource方法一样，这个if...else...判断也比较好理解：

如果自定义了名为"applicationEventMulticaster"的Bean，就实例化自定义的Bean，但自定义的Bean必须是ApplicationEventMulticaster接口的实现类
如果没有自定义名为"ApplicationEventMulticaster"的Bean，那么就注册一个类型为SimpleApplicationEventMulticaster的Bean

整个Spring的广播器是观察者模式的经典应用场景之一，这个之后有时间会分析Spring广播器的源码。

onRefresh方法

接下来简单说说onRefresh方法，AbstractApplicationContext中这个方法没有什么定义：

/**
 * Template method which can be overridden to add context-specific refresh work.
 * Called on initialization of special beans, before instantiation of singletons.
 * <p>This implementation is empty.
 * @throws BeansException in case of errors
 * @see #refresh()
 */
protected void onRefresh() throws BeansException {
    // For subclasses: do nothing by default.
}

看一下注释的意思：一个模板方法，重写它的作用是添加特殊上下文刷新的工作，在特殊Bean的初始化时、初始化之前被调用。在Spring中，AbstractRefreshableWebApplicationContext、GenericWebApplicationContext、StaticWebApplicationContext都实现了这个方法。

registerListeners方法

registerListeners方法顾名思义，用于注册监听器：

 1 /**
 2  * Add beans that implement ApplicationListener as listeners.
 3  * Doesn't affect other listeners, which can be added without being beans.
 4  */
 5 protected void registerListeners() {
 6     // Register statically specified listeners first.
 7     for (ApplicationListener listener : getApplicationListeners()) {
 8         getApplicationEventMulticaster().addApplicationListener(listener);
 9     }
10     // Do not initialize FactoryBeans here: We need to leave all regular beans
11     // uninitialized to let post-processors apply to them!
12     String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
13     for (String lisName : listenerBeanNames) {
14         getApplicationEventMulticaster().addApplicationListenerBean(lisName);
15     }
16 }

这里先向applicationEventMulticaster中注册一些静态的、特定的监听器。

finishRefresh方法

最后一步，结束Spring上下文刷新：

 1 /**
 2  * Finish the refresh of this context, invoking the LifecycleProcessor's
 3  * onRefresh() method and publishing the
 4  * {@link org.springframework.context.event.ContextRefreshedEvent}.
 5  */
 6 protected void finishRefresh() {
 7     // Initialize lifecycle processor for this context.
 8     initLifecycleProcessor();
 9 
10     // Propagate refresh to lifecycle processor first.
11     getLifecycleProcessor().onRefresh();
12 
13     // Publish the final event.
14     publishEvent(new ContextRefreshedEvent(this));
15 }

这里面分了三步，第一步，初始化LifecycleProcessor接口：

 1 protected void initLifecycleProcessor() {
 2     ConfigurableListableBeanFactory beanFactory = getBeanFactory();
 3     if (beanFactory.containsLocalBean(LIFECYCLE_PROCESSOR_BEAN_NAME)) {
 4         this.lifecycleProcessor =
 5                 beanFactory.getBean(LIFECYCLE_PROCESSOR_BEAN_NAME, LifecycleProcessor.class);
 6         if (logger.isDebugEnabled()) {
 7             logger.debug("Using LifecycleProcessor [" + this.lifecycleProcessor + "]");
 8         }
 9     }
10     else {
11         DefaultLifecycleProcessor defaultProcessor = new DefaultLifecycleProcessor();
12         defaultProcessor.setBeanFactory(beanFactory);
13         this.lifecycleProcessor = defaultProcessor;
14         beanFactory.registerSingleton(LIFECYCLE_PROCESSOR_BEAN_NAME, this.lifecycleProcessor);
15         if (logger.isDebugEnabled()) {
16             logger.debug("Unable to locate LifecycleProcessor with name '" +
17                     LIFECYCLE_PROCESSOR_BEAN_NAME +
18                     "': using default [" + this.lifecycleProcessor + "]");
19         }
20     }
21 }

流程和initMessageSource方法、initApplicationEventMulticaster方法基本类似：

先找一下有没有自定义名为"lifecycleProcessor"的Bean，有的话就实例化出来，该Bean必须是LifecycleProcessor的实现类
没有自定义名为"lifecycleProcessor"的Bean，向Spring上下文中注册一个类型为DefaultLifecycleProcessor的LifecycleProcessor实现类

第二步，调用一下LifecycleProcessor的onRefresh方法。

第三步，由于之前已经初始化了：

 1 public void publishEvent(ApplicationEvent event) {
 2     Assert.notNull(event, "Event must not be null");
 3     if (logger.isTraceEnabled()) {
 4         logger.trace("Publishing event in " + getDisplayName() + ": " + event);
 5     }
 6     getApplicationEventMulticaster().multicastEvent(event);
 7     if (this.parent != null) {
 8         this.parent.publishEvent(event);
 9     }
10 }

后记

再看AbstractApplicationContext的refresh方法，从中读到了很多细节：

Spring默认加载的两个Bean，systemProperties和systemEnvironment，分别用于获取环境信息、系统信息
BeanFactoryPostProcessor接口用于在所有Bean实例化之前调用一次postProcessBeanFactory
可以通过实现PriorityOrder、Order接口控制BeanFactoryPostProcessor调用顺序
可以通过实现PriorityOrder、Order接口控制BeanPostProcessor调用顺序
默认的MessageSource，名为"messageSource"
默认的ApplicationEventMulticaster，名为"applicationEventMulticaster"
默认的LifecycleProcessor，名为"lifecycleProcessor"

除了这些，在整个refresh方法里还隐藏了许多细节，这里就不一一罗列了，多读源码，会帮助我们更好地使用Spring。

posted @ 2017-04-07 19:51 五月的仓颉阅读(4612) 评论(7) 编辑收藏举报

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